1. Field of the Invention
The present invention relates to a data communication system, and more particularly to a data communication system capable of varying a transmission frame format corresponding to a data receiver in synchronous point-to-point communications or point-to-multipoint communications, and a data communication controller used therein.
2. Description of the Related Art
Communication equipment to date has mainly sent and received information that can be expressed in bits (SCN/SD data), such as alarm/device blocking (disengagement). By contrast, as a result of the appearance in recent years of Transmission Control Protocol/Internet Protocol (TCP/IP) and Asynchronous Transfer Mode (ATM) cells, the principal data being handled is becoming information that treats a plurality of information as a lump (information in which direct memory access (DMA) information is lumped together with SCN/SD data).
Further, communications are carried out in numerous modes, such as when communications are carried out between devices within an exchange and in a switching system, or a router and a small private branch exchange (PBX) located within a physical distance of around 100 m, or when system equipment such as switches are comprised of a plurality of printed board units, and data is transmitted between these printed board units, or synchronous communications are carried out between large-scale integration (LSI) mounted on a printed board unit.
FIG. 11 depicts a conceptual schematic, which illustrates communications of this kind. The figure indicates data communications being carried out between two printed board units 1, 2. Printed board unit 1 comprises a processor 10 and an LSI 11 controlled thereby.
Printed board unit 2, on the other hand, comprises a plurality of LSI 20 through 22, which receive the various data sent from LSI 11. In addition, each of the plurality of LSI 20 through 22 control corresponding controlled systems 23 through 25.
The data sent from LSI 11 of printed board unit 1 to LSI 20 through 22 of printed board unit 2 is sent by a synchronous-type communications format shown in FIG. 12.
That is, a frame pulse FP is generated in synch with a clock CLK. Each frame pulse FP comprises a single frame. As data, control information, such as frame header information, data stack monitoring information or a loop back signal (a line break monitoring pilot signal), is placed at the beginning of a frame.
Following the control information, SCN/SD data is also included. The meaning of this SCN/SD data is in bit units, and this information must be transferred in an emergency inside a device or system. For example, in-system alarm information and system switching information is utilized. Data characteristics are high speed/low volume.
Next, DMA data is included. A plurality of bits (for example, 16 bits or more) form a meaning of the DMA data, and which is low speed/high volume data, such as channel establishment information and rating information. Or, there is ATM setup information, which is held by software/firmware, and when data is written to and read from memory, a large quantity of DMA data is used.
Here, in a system previously developed by the inventors, the length of the above-described control information, SCN/SD data and DMA data are solidly fixed to the respective lengths of j clocks, k clocks and l clocks in the length (i clock length) of a single frame.
Also, as for the SCN/SD data and DMA data, the former has high velocity/low volume characteristics, and the latter has low velocity/high volume characteristics, as described above. Furthermore, the same data is not sent to all of a plurality of devices at the communication destination.
Therefore, in point-to-point communications, when the ratio of SCN/SD data and DMA data have differed for each destination device and each communication, a communication system/procedure had to be develop separately for each situation.
Also, with a view toward a switching system, the ratio of SCN/SD data and DMA data differs according to the size of the exchange and communication volume (for example, the alarm call volume), and with the above frame format, this ratio is fixed, which made it difficult to adequately change in accordance with exchange size and communication volume.